A liquid crystal display of light weight, thin thickness and low power consumption has been used in various information display terminals and visual equipments. The major operating mode for the liquid crystal display is the twisted nematic ("TN") and the super twisted nematic ("STN"). Although they are presently commercially used in various liquid crystal display means, the characteristics of narrow viewing angle are still remained unsolved. An In-Plane Switching ("IPS") mode liquid crystal display has been suggested to solve foregoing problems.
As described in FIG. 1, a plurality of gate bus lines 11 are formed on a lower insulating substrate 10 along an X direction shown in the drawings and they are parallel to each other. A plurality of data bus lines 15 are formed along an Y direction which is substantively orthogonal with the X direction. Therefore a sub pixel region is defined. At this time, a pair of gate bus line 11 and a pair of data bus line 15 are shown for defining the sub pixel region. The gate bus line 11 and the data bus line 15 are insulated by a gate insulating layer(not shown). A counter electrode 12 is formed, for example in a square frame shape, in a sub pixel region. At that time, the counter electrode 12 and the gate bus line 11 are disposed on the same plane. A pixel electrode 14 is formed at each sub pixel region where the counter electrode 12 is formed. The pixel electrode 14 is composed of a web region 14a which divides the region surrounded by the square frame type counter electrode 12 with the Y direction, a first flange region 14b connected to one end portion of the web region 14a and overlapped with the counter electrode 12 of X direction, and a second flange region 14c which is parallel to the first flange region 14b and is connected to another end portion of the web region 14a and overlapped with the counter electrode 12 of the X direction. That is to say, the pixel electrode 14 seems the letter "I". Here, the pixel electrode 14 and the counter electrode 12 are insulated by a gate insulating layer (not shown).
The thin film transistor(hereinafter TFT) 16 is disposed at the intersection of the gate bus line 11 and the data bus line 12. This TFT 16 is composed of a gate electrode being extended from the gate bus line 11, a drain electrode being extended from the data bus line 15, a source electrode being extended from the pixel electrode 14 and a channel layer 17 formed over upper of the gate electrode. A storage capacitor (Cst) is formed in the region where the counter electrode 12 and the pixel electrode 14 are overlapped. Though not shown in FIG. 1, an upper substrate (not shown) including a color filter(not shown) and a lower substrate 10 are oppositely and disposed with a predetermined distance. Further a liquid crystal layer(not shown) having a plurality of liquid crystal molecules is interposed between the upper substrate(not shown) and the lower substrate. Also, onto the resultant structure of the lower substrate and onto an inner surface of the upper substrate are formed homogeneous alignment layers, respectively. Before forming an electric field between the counter electrode 12 and the pixel electrode 14, the long axes of liquid crystal molecules 19 are arranged parallel to the surface of the substrate and therefore the orientation direction of the molecules 19 is decided. The R direction in the drawings is the direction of rubbing axis for the homogeneous alignment layer formed on the lower substrate 10.
A first polarizing plate(not shown) is arranged on the outer surface of the lower substrate 10 and a second polarizing plate(not shown) is formed on the outer surface of the upper substrate(not shown). Here the first polarizing plate is disposed to make its polarizing axis to be parallel to the P direction of the FIG.1. That means, the rubbing axis direction R and the polarizing axis direction P are parallel each other. On the other hand, the second polarizing plate is disposed to make its polarizing axis to be parallel to the Q direction which is substantially perpendicular to the polarizing axis of the first polarizing axis. When an scanning signal is applied to the gate bus line 11 and a display signal is applied to the data bus line 15, the TFT 16 disposed at the intersection of the gate bus line 11 and the data bus line 15 is turned on. Then the display signal of the data bus line 15 is transmitted to the pixel electrode 14 through the TFT 16. Consequently, an electric field E is generated between the counter electrode 12 inputted a common signal and the pixel electrode 14. At this time, as the direction of electric field is x direction as described in the FIG. 1, it has a predetermined degree of angle with the rubbing axis.
Afterwards, before the electric field is not formed, the long axes of the liquid crystal molecules are arranged parallel to the substrate surface and parallel to the long axis of the rubbing direction R. Therefore the light passed through the first polarizing plate and the liquid crystal layer is unable to pass the second polarizing plate, the screen has dark state. As the electric field is generated, the long axes(or optical axis) of the liquid crystal molecules are rearranged parallel to the electric field, and therefore the incident light passed through the first polarizing plate and the liquid crystal layer passed through the second polarizing plate and the screen has white state. At that time, the direction of the long axes of the liquid crystal molecules as being parallel to the substrate surface becomes changed according to the presence of the electric field. The characteristics of viewing angle are enhanced.
As well known, the refractive anisotropy(or birefringence: .DELTA.n) is occurred due to the difference of the lengths of the long and the short axes. The refractive anisotropy(.DELTA.n) is also varied from the observer's viewing directions. Therefore a predetermined color is appeared on the region where the polar angle is of 0 degree and azimuth angle range of degrees 0, 90, 180 and 270 in spite of the white state. This regards as the color shift and more detailed description thereof is attached with reference to the equation (1). EQU T.apprxeq.T.sub.0 sin.sup.2 (2.chi.).multidot.sin.sup.2 (.pi..multidot..DELTA.nd/.lambda.) (1)
wherein, T: transmittance;
T.sub.0 : transmittance to the reference light; PA1 .chi.: angle between an optical axis of liquid crystal molecule and a polarizing axis of a polarizer; PA1 .DELTA.n: birefringence; PA1 d: distance or gap between the upper and lower substrates (thickness of the liquid crystal layer); and PA1 .lambda.: wavelength of the incident light. PA1 a second substrate oppositely disposed to the first substrate with a predetermined distance; PA1 a liquid crystal layer including a plurality of liquid crystal molecules sandwiched between the first and second substrates; and PA1 polarizing plates attached to outer surfaces of the first substrate and the second substrate respectively; PA1 wherein each of unit cells defined by the adjacent two bus lines of the plurality of bus lines and the adjacent two scanning lines of the plurality of gate lines is divided into a plurality of electric field forming regions; and wherein the electric field formed in each electric field forming regions is obliquely formed toward the data bus line and the gate bus line, thereby having a symmetry with adjacent electric field forming region. PA1 a first substrate comprising of a plurality of data bus lines which are parallel each other; a plurality of gate bus lines disposed parallel to form matrix type unit cells; a plurality of thin film transistors disposed at the intersections of the data bus lines and the gate bus lines, each disposed at each unit cell; and a pixel electrode connected to each of thin film transistor and a counter electrode are formed in each unit cells of the first substrate; PA1 a second substrate oppositely disposed to the first substrate with a predetermined distance; PA1 a liquid crystal layer including a plurality of liquid crystal molecules sandwiched between the first and second substrates; PA1 homogeneous alignment layers formed over inner surfaces of the first and the second substrates, respectively; and PA1 polarizing plates attached to outer surfaces of the first substrate and the second substrate respectively; PA1 wherein the counter electrode of the first substrate includes a first electrode of a rectangular frame type forming an opening region surrounded thereby; at least one second electrode which divides the opening region surrounded by the first electrode into a plurality of squared aperture space, the second electrode being parallel to the gate bus line; and a common signal line transmitting a common signal to the first electrode; PA1 wherein the pixel electrode of the first substrate includes a first branch dividing the opening region surrounded by the first electrode to the direction parallel to the data bus line and a plurality of second branches which are crossed with the first branch to divide each of aperture spaces into four squared electric field forming regions; and PA1 wherein the electric field formed within the electric field forming region is disposed obliquely toward the gate bus line and the data bus line, thereby having a symmetry with adjacent electric field forming region. PA1 a first substrate comprising of a plurality of data bus lines which are parallel each other; a plurality of gate bus lines disposed parallel to form matrix type unit cells; a plurality of thin film transistors disposed at the intersections of the data bus lines and the gate bus lines, each disposed at each unit cell; and a pixel electrode connected to a thin film transistor and a counter electrode are formed in each of unit cells of the first substrate; PA1 a second substrate oppositely disposed to the first substrate with a predetermined distance; PA1 a liquid crystal layer including a plurality of liquid crystal molecules sandwiched between the first and second substrates; PA1 a first homogeneous alignment layer formed over an inner surface of the first substrate and having a rubbing axis parallel to the gate bus line(or the data bus line); PA1 a second homogeneous alignment layer formed over an inner surface of the second substrate and having a rubbing axis of 180 degrees with the rubbing axis of the first homogeneous alignment layer; PA1 a first polarizing plate attached to an outer surface of the first substrate and having a polarizing axis parallel to the rubbing axis of the first homogeneous alignment layer; and PA1 a second polarizing plate attached to an outer surface of the second substrate and having a polarizing axis being crossed with the polarizing axis of the first polarizing axis, PA1 wherein the counter electrode of the first substrate includes a first electrode of a rectangular frame type forming an opening region surrounded thereby; at least one second electrode which divides the opening region surrounded by the first electrode into a plurality of squared aperture space, the second electrode being parallel to the gate bus line; and a common signal line transmitting a common signal to the first electrode; PA1 wherein the pixel electrode of the first substrate includes a first branch dividing the opening region surrounded by the first electrode to the direction parallel to the data bus line and a plurality of second branches which are crossed with the first branch to divide each of aperture spaces into four squared electric field forming regions; and PA1 wherein the electric field formed within the electric field forming region is disposed obliquely toward the gate bus line and the data bus line, thereby having a symmetry with adjacent electric field forming region.
So as to obtain the maximum transmittance T, the .chi. should be .pi./4 or the .DELTA.nd/.lambda. should be .pi./2 according to the equation (1). As the .DELTA.nd varies with the birefringence difference of the liquid crystal molecules from viewing directions, the .lambda. value is varied in order to make .DELTA.nd/.lambda. to be .pi./2. According to this, the color corresponding to the varied wavelength .lambda. becomes appeared. Accordingly as the value of .DELTA.n relatively decreases in the viewing directions "a" and "c" toward the short axes of the liquid crystal molecules, the wave length of the incident light for obtaining the maximum transmittance relatively decreases. Consequently a blue color having a shorter wavelength than a white color is emerged. On the other hand, as the value of .DELTA.n relatively increases in the viewing directions "b" and "d" toward the long axes of the liquid crystal molecules, the wave length of incident light relatively increases. Consequently, a yellow color having a longer length than the white color is emerged. This causes deterioration of the resolution in IPS-LCDs.